I began seeing a difference fairly quickly, but it took several weeks for me to really get energy again. Watch the folic acid levels if you begin to have insomnia. I had to lower mine because I would take a shot and be up for a couple of days. Boy did I ever get a lot accomplished over those couple of days, though!

I haven't had shots but I did take a B complex with folic acid for a while, and it did help especially with the brain fog and fatigue - almost immediately for me. But I wasn't sick for long before going gluten free (a month of D more or less). I think my levels are ok nowadays though because I started having a bit of insomnia as well. Nowadays I just take a pill if I've recently been glutened and need to be able to work.